I think each individual has to decide for their-self what IT really is and perhaps IT changes as the individual grows in their training and life experiences.
Right now for me IT is connection and being able to feel and respond to that both as Uke and as Nage.
Have you read Ellis Amdur's new book?
There are specifics for "IT", aka Internal Training. If you're interested in learning more, read Ellis' book and/or peruse some threads in the Non-Aikido Martial Traditions forum. There are quite a bit of posts out there about "IT", aiki, Internal Skills (IS), etc. I hope you keep an open mind and read.